砾岩

例句：

1. 1. The road waspaved with gravel to improve drainage.
   为了改善排水，这条路铺了砾石。
2. 2.The construction crew used gravel to level thesite.
   施工队用砾石平整场地。
3. 3.The riverbed is covered in a layerof smooth gravel.
   河床覆盖着一层光滑的砾石。